.. It's because there is nothing behind level 4, so if I didn't add this barrier you would have fallen into the deep and dark black hole I put viciously in the source code.
In fact, there's a GAME OVER when you lose, but not when you won, so.. You may want to repeat playing level 4 as long as I don't add levels
(pliz give ideas for new moles to add at each level, and a bit data about them.)
